Bone plate systems provide fixed-angle fixation, by means of associated screws, of a bone plate for osteosynthesis in the bodies of humans or animals, Numerous bone plate systems are known that generally include a bone plate with an arrangement of several through-holes and associated screws, In addition to so-called bone screws, i.e., screws that are screwed into the bone during the fixation process, provision can be made of fastening screws that are themselves not screwed into the bone but into a thread formed in the bone plate. Such fastening screws are then used, for example, for fixing the bone screws (see for example Documents EP 1 702 577 A2, WO 2006/014438 A1 and also AT 406 446 B). In the system for cervical vertebrae in Document DE 698 35 968 T2, use is also made of a fastening screw for affixing several bone screws.
A bone plate provided with oblong holes is disclosed in Document WO 20051041769 A1.
Fixed-angle plate-screw connections to osteosynthesis plates have the advantage of better anchoring of the bone plate to the bone. This is particularly advantageous with fractures near joints, as in this manner it is possible, to grip and fix bone fragments near joints more effectively. The advantage of fixed-angle plate-screw connections is even more significant in the case of osteoporotic fractures near joints because non-fixed-angle bone screws are unable to affix an osteoporotic bone as effectively.
Fixed-angle plate-screw connections can be classified as monoaxial and polyaxial plate-screw connections.
Examples of monoaxial fixed-angle plate-screw connections are given in Documents DE 10 2005 044 841 B4 or DE 10 2005 043 285 E33. These systems are characterized in that they have screw heads with male threads that intermesh with corresponding female threads of plates. If a screw is screwed in during an operation, the positive fit between the male thread of the screw head and the female thread of the bone plate effects a fixed-angle plate-screw connection during the last turns of the screwing-in process.
Furthermore, bone plate systems have been proposed in which bone screws are variable with respect to their swivel or angular position relative to the bone plate during use. Such a bone plate system is described, for example, in document DE 10 2006 000 948 A1, A bone plate having at least one screw for fixed-angle fixation is disclosed in document WO 2007/025520 A1, Another example of a polyaxial fixed-angle plate-screw connection is disclosed in DE 10 2005 042 766 B4. The embodiment described therein of a female thread from six female thread columns makes it possible to screw in spherical head screws having a special male thread in the polyaxial direction and to affix them in a fixed-angle manner during the last turns of the screwing-in process. Such plate-screw systems have become increasingly common in clinical practice due to clinical advantages of a polyaxial fixed-angle fixation option.
Document WO 2010/115403 A1 discloses a device for the fixed-angle fixation and compression of a fracture site on a bone. The disclosed bone plate is equipped with several individual holes, in each of which a bone screw can be screwed in. In combination with the individual holes, provision can be made for equipping the latter with a crescent-shaped hole extension,
Document WO 2009/058969 A1 also relates to a bone plate system in which the bone plate is equipped with several individual holes for holding exactly one screw in each case. In the through-holes provision is made of columns with projections that, in the screwed-in state of the respective screw, intermesh with a thread on the screw head. The plurality of columns with projections are separated from one another in the respective hole by areas that are free from such projections and hence have a smooth surface.
Additionally, a bone plate system for osteosynthesis is disclosed in Document WO 2011/076205 A1 in which for affixing the bone plate to the bone a swivel screw is screwed into a swivel hole and a clamping screw is screwed into a clamping hole in such a way that, in the screwed-in state, the swivel screw and the damping screw are affixed at a fixed angle in many dimensions, the screw heads of the swivel screw and of the damping screw being secured against a relative motion in relation to one another and in relation to the bone plate, wherein the swivel screw and the clamping screw are each configured as a bone screw.
Additionally, Document DE 10 2007 005 417 A1 discloses a plate implant for use on the spinal column, in which each bone screw is screwed into an associated through-hole. The screw head of the bone screw is equipped with a thread that, in the screwed-in state, cooperates with intersecting lines or intersecting surfaces in each associated through-hole.